Key message

Distributions of water- and air-filled conduits can be distinguished by observing a xylem cross-section of frozen conifer stem. This method is applicable to field observation in cold winter.

Abstract

Xylem embolism resulting from summer drought and frost drought is one of the critical stresses responsible for the dieback of stems and individuals of subalpine evergreen conifers. The occurrence of xylem embolism in conifers depends not only on the species but also on the plant microhabitats, causing difficulties in understanding possible adaptive strategies against xylem embolism. This study examines a simple method of using a digital camera to photograph the xylem water distribution (CXW method) in cross-sections of frozen stems. Light is transmitted through the water-filled tracheid lumen but reflects and scatters at the surface of embolized tracheids, resulting in contrast in wood color between darker (water-filled tracheids) and lighter (air-filled tracheids) colored regions. The CXW method was effective in detecting water distribution in conifers, although the colored xylem in latewood and reaction wood decreased the color contrast between air- and water-filled regions. By cutting the frozen stem with a cryostat, sequential changes in the water distribution of stem xylem were easily monitored. In the cold winter of the subalpine region, the spatial distribution of embolized conduits can be detected when a branch is collected. If a cryostat is available, this method is applicable to other tracheid-bearing wood collected in any season and does not require additional instruments or time-consuming intensive labor in the field. Information about the hydraulics of conifers growing in extreme environments contributes to the understanding of their adaptive strategy and facilitates accurate prediction of forest dynamics under future climatic conditions.

中文翻译：

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一种观察亚高山针叶树气管木材中水分分布的简单方法

关键信息

通过观察冷冻针叶树茎的木质部横截面，可以区分出充满水和充满空气的导管的分布。该方法适用于寒冷冬季的野外观测。

抽象

夏季干旱和霜冻干旱引起的木质部栓塞是导致亚高山常绿针叶树茎和个体枯萎的关键压力之一。针叶树中木质部栓塞的发生不仅取决于物种，而且还取决于植物的微生境，从而导致难以理解针对木质部栓塞的可能的适应策略。这项研究探讨了一种使用数码相机拍摄冷冻茎横断面上木质部水分分布的简单方法（CXW方法）。光穿过充满水的气管腔，但在栓塞的气管表面反射并散射，从而导致深色（充满水的气管）和较浅（充满空气的气管）区域之间的木材颜色形成对比。CXW方法可有效检测针叶树中的水分分布，尽管红木和反应木中的有色木质部降低了空气和水充满区域之间的色差。通过用低温恒温器切割冷冻的茎，可以容易地监测茎木质部的水分布的连续变化。在亚高山地区的寒冷冬季，收集分支时可以检测到栓塞导管的空间分布。如果有低温恒温器，则该方法适用于任何季节收集的其他含气管的木材，并且在现场不需要额外的仪器或费时的密集型劳动。